In bone surgery it is well known to apply longitudinal implants like bands, braids, or wires to fixation of bone fragments to each others. Such implants are made usually of metals or of polymeric materials.
Chest surgery such as, for example, open heart surgery requires opening of the chest and rib cage in order to facilitate access to the organ to be operated. The front central part of the rib cage constitutes a longitudinal bone, the sternum, which overlies the heart and secures the ribs. A specific action performed in such surgery is longitudinal sectioning of the sternum into two halves (“median sternotomy”). After performing the heart surgery, the chest is closed as a part of a reconstitution operation, in which among other activities the sternum bone halves are brought to union and secured together by mechanical means.
Post operative complications in the healing of the sternum are not uncommon, resulting from several reasons. Especially troublesome is the constant movement associated with the breathing cycle, to which the bone is subjected, which keeps the sternum in a cyclic strain regime often accompanied by unpredicted mechanical stresses. Such strains may eventually cause non-union or breakage of the bone. Nowadays as recuperating procedures for cardiac therapy have become more common, sternal complications have been increasing likewise. Healing disorders can be expected to occur more commonly in patients suffering from bone disorders such as osteoporosis.
Surgical band and locking member systems position cables and locking implants around bones to allow healing. One common form of a locking implant is a crimp system. These systems are used to crush the cable into engagement with the tissue to retain the cable at a desired position. However, current designs of cable and crimp systems, particularly for surgical use, have significant drawbacks. For example, a tension, which is too low or too high may lead to improper healing or to poor medical results.
Also, in many prior art cable and crimp systems there is the possibility for slippage of the cable in the crimp, which can lead to delayed healing. The loosening of the cable, e.g. in bone fracture fixation, can also lead to delayed healing, pain or even to a failure of healing. Also, many prior art crimps cannot be easily locked at a desired tension, and often the desired tension can not be maintained when using a cable loop or winding as there is an inevitable drop in tension when the pliers are removed. Thus, a surgeon typically has to “over shoot” the desired tension, guessing how much of that tension will be lost after the crimping has been completed and the pliers removed, thus significantly increasing the possibility for tensioning errors.
In addition, many prior art crimps are bulky and may cause adverse tensioning in the surrounding tissues, which may result in a negative effect on tissue healing. Another drawback of many prior art cable and crimp systems is that they are made of metal, such as stainless steel. Such extremely stiff materials are mechanically incompatible with bone tissue and therefore, may cause osteolysis below the material, which may lead to implant migration.